1. Field of the Invention
The invention relates to an image forming apparatus using an electro-photographic process, such as a printer or a copying machine. In particular, the invention relates to an image forming unit for forming a developed image by supplying toner to an electrostatic latent image formed on a surface of an image carrier.
2. Description of the Related Art
In general, a toner for developing an electrostatic latent image formed on the surface of an image carrier is formulated to have a predetermined glass transition temperature. This glass transition temperature is set to ensure melting of the toner by heat supplied from a fixing unit. In a case where an image forming unit filled with a toner having such a predetermined glass transition temperature is stored for a long period of time, the toner may soften or melt and thus form an adhering or clumping together in a nip formed between a development roller and a development blade, another nip formed between the development roller and a supply roller, or other similar parts. Such a situation may occur, for example, during a period starting with the post-manufacturing quality inspection of the image forming unit, through shipment from the plant, and ending with a user's actual use of the image forming unit.
If an adhering or clumping formed from a softened or melted part of the toner enters a nip formed between, for example, the development roller and the development blade, such material makes a gap between the developing roller and the developing blade. Leakage of the toner from the gap thus formed produces a defective image.
An image forming unit according to the related art includes: a toner container for containing toner; a development roller rotatably supported by this toner container; a sealing member for sealing a longitudinal end portion of a circumferential surface of the development roller by being in contact with the longitudinal end portion of the circumferential surface of the development roller. In this image forming unit, a sealing toner having a glass transition temperature higher than a toner used for development is applied to a contact area between the development roller and the sealing member.